Considering a first influenza (flu) vaccination is a common and important health decision. Understanding the reasons for vaccination, how it works, and what to expect can help you make an informed choice.
Why Vaccination Matters
Influenza is a respiratory illness caused by viruses that infect the nose, throat, and lungs, often leading to serious complications. These can include pneumonia, bronchitis, inflammation of the heart or brain, and respiratory failure. Even healthy individuals can experience severe illness from the flu.
Receiving a flu vaccine reduces the risk of contracting the flu and, if infection still occurs, lessens symptom severity, complications, and the likelihood of hospitalization or death. Vaccination has been shown to reduce the risk of flu-related intensive care unit (ICU) admission by 26% and death by 31% among hospitalized adults. Beyond personal protection, vaccination contributes to community health by creating “herd immunity,” which helps protect vulnerable populations. This includes infants too young to be vaccinated, older adults, and individuals with weakened immune systems.
A new flu shot is necessary each year because influenza viruses constantly change, and protection from a previous year’s vaccine can decline. Scientists predict which flu strains are most likely to circulate, and the vaccine is reformulated annually to target these viruses. This ensures effective protection against prevalent strains.
How the Flu Shot Works
The flu shot contains inactivated (killed) virus particles or components, or in the case of the nasal spray vaccine, a weakened live virus. These components are not capable of causing influenza illness. Instead, they introduce the body’s immune system to specific proteins from the influenza virus.
Upon vaccination, the immune system recognizes these viral components as foreign and begins to produce antibodies. These specialized proteins identify and neutralize the flu virus if the body encounters it in the future. This process effectively “teaches” the immune system how to fight off the virus without experiencing the full illness.
It takes about two weeks after vaccination for the body to develop a sufficient antibody response and establish immunity. During this period, it is still possible to contract the flu if exposed. Common, mild side effects include soreness, redness, or swelling at the injection site, a low-grade fever, or muscle aches, usually resolving within one to two days. These mild symptoms indicate the immune system is actively building protection.
Common Questions and Considerations
The ideal time to receive a flu shot is in September or October, before flu activity increases. However, getting vaccinated later in the flu season, which can extend into May, still offers beneficial protection. It is always better to get vaccinated late than not at all.
Most individuals aged 6 months and older are recommended to receive a seasonal flu vaccine annually. Certain groups particularly benefit due to a higher risk of serious complications. These include adults aged 65 and older, young children, pregnant individuals, and people with chronic health conditions like asthma, diabetes, heart disease, or weakened immune systems.
There are rare instances when someone should not get a flu shot or should consult a healthcare provider first. These include individuals with a severe, life-threatening allergy to any vaccine component or those who experienced Guillain-Barré Syndrome within six weeks following a previous flu vaccination. A healthcare provider can assess individual circumstances and provide guidance.
A common misconception is that the flu shot can cause influenza. The injected flu shot contains inactivated virus or viral components, which cannot cause the flu. Mild, flu-like symptoms that sometimes occur after vaccination are a sign of the immune system responding and building immunity, not an actual flu infection. Another misconception is that one doesn’t need the vaccine if they rarely get sick; however, the flu can still cause severe illness even in otherwise healthy individuals. Consulting a healthcare provider can address any remaining concerns.